The measurement of circuit components is fundamental in all phases of work involving electricity and electronics. Traditionally, one of the most versatile instruments has been the hand held multimeter originally available in commercial form in a hand held case. Such a device was generally provided with various scales for reading both AC and DC voltage and both AC and DC current; for these measurements, the instrument received its power directly from the external AC or DC source. The instrument used an internal battery to actuate a galvanometer type meter indicator in order to measure passive quantities such as resistance. Since the source of voltage for such instruments was a battery, the arrangement of the circuits necessary for such measurements was straightforward and the instruments usually provided a wide range of scales for measuring and indicating each of these circuit values.
Generally, however, the original multimeters were incapable of measuring passive AC impedance quantities such as inductance and capacitance because only a DC voltage source was available and, in the prior art, the measurement of capacitance and inductance values has generally been accomplished by means of an AC bridge circuit. This conventional circuit uses either an external or internal AC signal source (typically operating at frequencies of a thousand Hertz, for example) to operate a bridge circuit, one leg of which contained the unknown AC impedance. Such bridge circuits are complicated by the fact that they require the presence of an AC signal source and further they require the bridge to be balanced and that, in turn, requires a calibrated AC impedance of like kind to that which is being measured.
In some modern versions of the multimeter circuit, a digital circuit with digital readout has been provided for giving an accurate reading of the same DC quantities and some of these units are capable of measuring AC impedances. However, these more modern circuits still use the conventional bridge technique to measure the impedances with the attendant problems discussed above.